Device for applying a coating substance to a continuous paper web

ABSTRACT

The invention relates to a device for applying a coating substance to a continuous paper web in a process for producing abrasion-resistant laminates for manufacturing decorative paper. The coating substance consists of a viscous mixture of melamine resin and alphacellulose to which particles of corundum are added, and is applied to the visible surface of the paper. The inventive device includes a deflector roll ( 2 ) on which the paper web ( 1 ) lies in an area in which it loops around; a metering roll ( 6 ) which is arranged parallel to the deflector roll ( 2 ) and forms the boundary of a gap with the same, and which is driven synchronously or almost synchronously with the deflector roll; a slit nozzle ( 7 ) for applying the coating substance either directly to the paper web ( 1 ) on the deflector roll ( 2 ) or to the metering roll ( 6 ); and a doctor blade of a rectangular piece ( 9 ) of flexible rubber type material. This material is fixed on one side by its back edge, parallel to the axes of the two rolls ( 2,6 ) and lies loosely on the upper end of the paper web ( 1 ) running off of the deflector roll ( 2 ).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US nation phase of PCT applicationPCT/EP99/01946 filed Mar. 1999 with a claim to the priority of Germanpatent application 19814212.9 itself filed Mar. 31, 1998 Germanapplication 19825156.4 itself filed Jun. 5, 1998.

FIELD OF THE INVENTION

The invention relates to a device for applying a coating substance,comprised of a liquid resin and a fine-grained abrasive material,especially corundum, to a continuous paper web for use in the productionof wear-resistant laminates.

BACKGROUND OF THE INVENTION

DE 95 08 797 C1 describes a process for producing decorative paper foruse in the production of wear-resistant laminates. For this purpose, aviscous mixture of melamine resin and alpha cellulose to which corundumparticles have been added is deposited as a coating substance on thevisible surface of a decorative paper.

The alpha cellulose serves, therefore, as a stiffening and suspendingagent. The corundum particles have a grain size of 15 to 50 μm. Thecoating quantity amounts to 80 to 200 g/m² so that, after attaining thefinal moisture content, the layer thickness is 20 to 60 μm. The coatingsubstance should be applied by means of a wire doctor element, a reversecoating system or a screen roller.

It has been found in practice that any moving parts of such coatingsubstance which come into contact with the coating substance are wornout in very brief periods of time by the abrasive corundum.

In the submission of H. Peters which appeared in the journal “Weakly forpaper fabrication”, 6, 1973, p. 164 to 169, a nozzle coating system,inter alia, has been briefly described. In that system, a slit nozzle istrained from below on a lower region of a continuous cardboard web whichis looped around a rotating roller in a hairpin shape. Downstream of thenozzle, in the movement direction, a doctor blade is arranged to smoothout the applied layer and for removal of surplus coating substance. Fromthis publication one learns that the coating device is suitable forcoating quantities up to 25 to 30 g/m² and is especially advantageous athigh speeds.

OBJECTS OF THE INVENTION

It is the object of the invention to provide a device for applying acoating substance comprised of liquid resin and fine-grained abrasivematerial, especially corundum, to a continuous paper web which satisfiesthe following requirements:

On the one hand, the coating substance should be applicable in arelatively thick uniform layer as is required for papers which areintended for the production of abrasion-resistant laminates, especiallywith a coating quantity of 80 to 200 g/m².

On the other hand, the device should largely avoid the need forexpensive machine components which are subject to excessive wear by theabrasive particle.

This object is attained with the device of applying a liquid resin andfine-grained abrasive material, especially corundum onto a continuouspaper web for use in the production of abrasion resistant laminates. Thedevice according to the invention is provided with a deflecting rolleron which the paper web lies in a looping region, with a metering rollerwhich is arranged parallel to the deflecting roller and includes anarrow gap therewith and is driven synchronously or approximatelysynchronously with the deflecting roller, with a slit nozzle forapplying the coating substance either directly to the paper web lying onthe deflecting roller or to the metering roller, and with a doctor bladecomprised substantially of a rectangular flap of a flexible rubber likematerial which is affixed at its rear edge parallel to the axes of thetwo rollers and which lies slackly on the upper pass departing from thedeflecting roller of the paper web.

The uniformity of the applied coating is still further improved byaffixing the flap to a support bar which is set into vibration.

The slit nozzle is oriented from above onto the metering roller to allowthe coating substance which is applied to the metering roller to be morereadily observable. This simplifies the predosing. Since in thisarrangement the nozzle slit lies below, the device can be operated withlower pump pressures. The settling of particles in the nozzle iscompletely avoided.

When the slit nozzle is offser reative to the zenith line of themetering roller in the direction of rotation of the metering roller itis possible to avoid running of the coating substance into the rollergap upon standstill of the machine and smearing of the deflectingroller.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing serves to illustrate the invention based upon embodimentsschematically illustrated in FIGS. 1 to 3.

SPECIFIC DESCRIPTION

A paper web 1, which is already preimpregnated with resin and optionallyhas already been dried, is fed according to FIG. 1 in a horizontaldirection beneath a deflecting roller 2. It is looped around thedeflecting roller 2 to form an arc through 180° which is bounded on oneside by an approach line 3 and on the other side by a departure line 4.Then it runs in a horizontal direction as is symbolized by arrow 5 to adrier that is not shown.

A metering roller 6 is arranged adjacent the deflecting roller 2 and hasa smooth roller surface. It has in this embodiment the same diameter asthe deflecting roller 2. The axes of the deflecting roller 2 and trhemetering roller 6 are journaled in a machine frame parallel to oneanother at the same level. The bearings of one of the two rollers 2 and6 are journaled in a machine frame parallel to one another at the samelevel. The bearings of one of the two rollers 2 and 6 are shiftableparallel to the horizontal direction so that the width of the narrow gapbetween the two rollers 2 and 6 can be varied. The metering roller 6like the deflecting roller 2 is provided with a drive. The drives forthe two rollers 2 and 6 can be mechanically or electrically coupled sothat the rollers 2 and 6 run synchronously or approximatelysynchronously.

Below the deflecting roller 2, a slit nozzle 7 is arranged for applyingthe coating substance. The nozzles's slit is adjacent the approach line3.

Above the deflecting roller 2 a support bar 8 parallel to the axes ofthe two rollers 2 and 6 is connected with the machine frame. On thesupport bar 8, the rearward edge of a rectangular flap 9 extending inthe direction of the arrow 5 and formed of a flexible rubber-likematerial is affixed, the flap extending over the full working width,i.e. the width of the coated paper web 1. The remaining edges of therectangular flap 9 are free. The flap 9 lies like a slack strip over itspart opposite the support bar 8 on the upper pass of the paper web 1travelling awat from the defecting roller 2 in the region of thedeparture line 4. The length of the flap 9—in the direction of the arrow5—is about between 5 and 50 cm, preferably between about 10 and 30 cm.The flap 9 is approximately 2 to 5 mm thick.

In operation, the paper web 1 travels with a speed between about 10 and70 m/min, preferable between 20 and 50 m/min. With the slit nozzle 7,the coating substance is coated from below onto the paper web 1 inexcess, the coating substance consisting of liquid resin and finecorundum particles suspended therein. The thus applied layer is split inthe narrow gap between the deflecting roller 2 and the metering roller 6so that a part of the coating substance remains adherent to the paperweb 1, another part being entrained by the metering roller 6. Surpluscoating substance is dammed up in the gap and drops down. Since thesurface speeds fo the two rollers 2 and 6 are at least approximately thesame, the abrasive particles contained in the coating mass do notnoticeably wear on the metering rolller 6.

The layer adherent to the paper web 1, on an average about 80 to 200g/m² is initially nonuniform so that longitudinal strips are clearlyvisible. Their widths amount as a rule to about 5 mm. The spacing of thestrips from one another is at most between about 10 and 30 mm. Theundesired strip pattern changes in an unpredictable way. It is easilyequalized by the flap 9 which presses with friction against the paperweb 1 lightly so that such strips practically no longer arise. In astationary state none of the coating substance is thereby stripped away.The flap 9 thus has only a comparatively minor effect and does not actas a metering element. It is naturally engaged by the abrasive particlesand must thus be replaced from time to time. This replacement isrelatively simple and does not contribute to any significant cost.

The embodiment of FIG. 2 differs from the afore-described embodimentespecially in that the slit nozzle 7 is trained ont he surface of themetering rollr 6. The coating substance deposited on the metering roller6 is transferred in the gap between the two rollers 2 and 6 to passpartly onto the paper web 1. The two embodiments otherwise are inagreement with one another such that further explanation of FIG. 2 issuperfluous.

In the embodiment shown in FIG. 3, the slit nozzle 7 is arranged abovethe metering nozzle 6 so that the coating substance is applied fromabove. It is somewhat offset from the zenith line of the metering roller6 in the rotational direction. In the drawing it is locatedsubstantially in the eleven o'clock position.

The support bar 8 is bendable or connected by yieldable fasteningelements with the machine frame (not shown) so that it can make smallmovements relative to the machine frame. On the support bar 8 there ismounted a compressed-air turbine vibrator 10. It is comprised mainly ofa block-shaped housing with a cylindrical hollow in which a rotor 11 isrotationally journaled so that its axis of rotation is oriented parallelto the support bar 8. It is provided with an eccentric weightsymbolically shown in the drawing by a black color sector. On thesurface of the rotor 11 there are radial ribs comparable to the bladesof a Pelton turbine. Two passages 12 and 13, whose axes are tangentialto the rotor 11, open on opposite sides in the interior of the vibrator10. The passage 12 is connected with a compressed-air source. Thepassage 13 is the outlet for the discharge air and is optionallyprovided with a sound damper that is not shown.

In operation, the vibrator 10 is supplied via the passage 12 withcompressed air. As a consequence, the rotor 11 is set into rotation,Because of the ecxcentric weighing of the rotor 11, circularoscillations are generated and transmitted to the support bar 8. Theflap 9 is therby set into vibration. The frequency of vibration isdetermined by the pressure of the supplied air which lies preferablybetween 100 and 200 Hz.

Suprisingly, it has been found that the equalizing effect of the flap issignificantly improved by the vibrations.

Elements for premetering or smoothing the coating substance entrained bythe metering roller 6 are not provided along the path between the slitnozzle 7 and the gap between the two rollers 2 and 6.

What is claimed is:
 1. A device for applying a coating substanceconsisting essentially of a liquid resin and fine-grained abrasivematerial onto a continuous paper web for use in the production of anabrasion-resistant laminate, the device comprising: a deflecting rollerrotatable about an axis and over which the paper web passes in a traveldirection in a looping region; a metering roller forming a gap with thedeflecting roller at the looping region and rotatable about an axisgenerally parallel to the deflecting-roller axis; means for generallysynchronously rotating the deflecting roller and metering roller aboutthe respective axes; means including a slit nozzle adjacent the rollersfor applying the coating substance to the paper web in the loopingregion; and a generally rectangular flap of a flexible rubber-likematerial having a rear edge fixed generally parallel to the axesadjacent the two rollers and lying slackly on the web downstream in thetravel direction of the region.
 2. The coating-applying device definedin claim 1, further comprising a support bar which extends generallyparallel to the axes and to which the flap rear edge is secured; andmeans for vibrating the support bar.
 3. The coating-applying devicedefined in claim 2 wherein the support is vibrated in a directionperpendicular to the support bar.
 4. The coating-applying device definedin claim 3 wherein the vibrating means includes a rotating eccentricweight.
 5. The coating-applying device defined in claim 3 wherein thevibrating means includes a compressed-air turbine.
 6. Thecoating-applying device defined in claim 1 wherein the slit nozzle isoriented above and directed downward onto the metering roller.
 7. Thecoating-applying device defined in claim 5 wherein the slit nozzle isoffset upstream in the travel direction to an uppermost portion of themetering roller.